Unfortunately, we’re probably underestimating the impact that fishing is having on ray populations. Although some will survive capture, we know little about the non-lethal and long-term effects of that stressful experience.

Included in those unknowns are questions relating to reproduction. In particular, what if the captured ray was pregnant? Would she still give birth? If she did, would her offspring survive?

Beyond just this species, our results suggest it’s possible that other ray and shark species that have live-birth (including most large sharks) could be similarly affected.

All rays give birth to live young. For many species pregnancy lasts about a year, making them more likely to be captured during reproduction compared to egg-laying species.

A makeshift maternity ward

Pregnant southern fiddler rays were collected by hand in Swan Bay, Victoria, Australia, using SCUBA to minimise stress during collection. They were transported and housed in our “maternity ward” – a large outdoor research facility located nearby.

Our maternity ward included a large tank equipped with a giant paddle that pushed water past stationary nets, thereby simulating a trawl net being dragged by a boat. Rays were placed in these nets and trawled, followed immediately by 30 minutes of air exposure to replicate the process of sorting the catch on board a boat. A similar number of control females were kept in a separate tank and were not subjected to trawling or air-exposure.

Over the next three months, pregnancy and the health of each mother was regularly monitored via ultrasounds, blood-sampling and weighing. At birth, their pups were also measured for length, weight and had their blood sampled. Mothers carried and gave birth to an average of two pups.

It’s tough out there for the little guy

Pups from trawled mothers were 12% shorter and 27% lighter than those from untrawled mothers.

Lower body mass may mean pups have fewer energy reserves – in the form of an internal yolk sac – to rely on. An increased risk of starvation is possible during the early stages of life when inexperience can make catching prey difficult.

Pups from trawled mothers also showed signs of a stress response in their immune system, and increased vulnerability to infection and disease is possible. The increased energy needed to maintain a healthy immune system may also limit growth rates. This is important for female fertility because larger females tend to carry more offspring.

The bigger picture – fishing for the future

By examining the non-lethal responses to capture stress, we’re working towards more efficient fishing practices that improve conservation outcomes for marine species.

A simulation of how bottom-trawling nets operate at sea.

Regarding reproduction, it may mean that we can better assess and manage fishing practices in areas where sharks and rays are known to congregate and breed. Fishing techniques that reduce the amount of accidental capture of rays and sharks will benefit both fishermen and conservation efforts, especially during vulnerable breeding periods.

For example, “turtle exclusion devices” in trawl nets (originally designed to prevent the capture of sea turtles) allow animals that are much bigger than the target catch to escape through a chute. Such a device may be suitable for reducing shark and ray bycatch too.

How a turtle exclusion device (TED) works.

Our study into how capture affected pregnancy in rays is part of a larger research program led by Monash University in collaboration with Flinders University, University of Tasmania and the Victorian Marine Science Consortium. The research program’s results on both lethal and non-lethal outcomes of capture have helped inform the Australian Fisheries Management Authority (AFMA) how to fish for the future and improve the conservation of sharks and rays.

An international team of astronomers has discovered that the supermassive black hole at the centre of our galaxy might be the source of mysterious high-energy cosmic rays that bombard the Earth on a daily basis.

The discovery, reported in Nature, brings new answers to one of astronomy’s most longstanding mysteries.

Back to the source

In 1912 Victor Hess found that the Earth was being bombarded by subatomic particles travelling at tremendous speeds that originated from outer space. He called the particles “cosmic rays”. But the origin of these high energy particles has remained a mystery for more than 100 years.

“How cosmic rays are created and accelerated at very high energies is the big question astronomers are trying to understand,” said Associate Professor Gavin Rowell, an astrophysicist from the University of Adelaide, who was involved in the Nature study.

One theory was that cosmic rays are produced during supernova explosions. These create “remnants” that send shock waves throughout the galaxy. This electrically charges particles in space, which are then accelerated to near the speed of light, eventually hitting the Earth.

However, because the particles are mangetically charged, any magnetic field in space will change their direction. That means it’s difficult to determine their origin once they strike our atmosphere.

In this study, the researchers used the High Energy Spectroscopic System (HESS) telescopes in Namibia to look for the very fast flashes of light created when cosmic rays collide with the Earth’s atmosphere.

Using this data, the researchers were able to estimate the direction of the cosmic ray, and found it pointed back towards the centre of our galaxy.

This coincides with the location of what is believed to be a supermassive black hole, with a mass of 4 to 5 million solar masses. The HESS team suggest that the huge gravitational force exerted by the tremendous mass of the black hole was able to accelerate the particles to their incredibly high velocities.

“This result adds a new dimension in cosmic rays, and how the cosmic rays our galaxy is producing could also come from this massive central black hole,” Rowell said.

Cosmic Cluedo

Professor Geraint Lewis, an astrophysicist at the University of Sydney, emphasised that the study also makes us aware that the universe can do things that far outstrip what we are capable of here on Earth. However, our understanding of cosmic rays is still far from complete.

He mentioned that the biggest question is explaining the precise cause of the particle acceleration.

“It is like a game of Cluedo: they’ve tied down what they think is the site of the murder, but now they are trying to locate the weapon,” he told The Conversation.

What it does tells us is that the cosmos can accelerate particles to velocities that far exceeds what we are capable doing on Earth.

“These particle accelerators in outer space put the Hadron Collider in the shade,” he said.